-- ? 錯誤：遺漏分號
SELECT name FROM user
SELECT age FROM user

-- ? 正確：每條語句結(jié)尾加英文分號
SELECT name FROM user;
SELECT age FROM user;

-- 假設(shè)表名是user，字段名是name、age
-- ? 錯誤：表名拼錯（user寫成users）、字段名拼錯（age寫成agee）
SELECT name, agee FROM users;

-- ? 正確：和創(chuàng)建時的表名、字段名完全一致
SELECT name, age FROM user;

-- ? 錯誤：SELECT寫成SELEC、INSERT寫成INSER
SELEC name FROM user;
INSER INTO user (name) VALUES ('張三');

-- ? 正確：關(guān)鍵字拼寫完整
SELECT name FROM user;
INSERT INTO user (name) VALUES ('張三');

-- ? 錯誤1：字段3個，值2個（數(shù)量不匹配）
INSERT INTO user (name, age, gender) VALUES ('張三', 20);

-- ? 錯誤2：字段順序和值順序不一致（name對應(yīng)20，age對應(yīng)'張三'）
INSERT INTO user (name, age) VALUES (20, '張三');

-- ? 正確：字段和值數(shù)量、順序完全一致
INSERT INTO user (name, age, gender) VALUES ('張三', 20, 1);

-- ? 錯誤：無WHERE條件，修改全表用戶年齡
UPDATE user SET age = 20;

-- ? 錯誤：無WHERE條件，刪除全表數(shù)據(jù)
DELETE FROM user;

-- ? 正確：加WHERE條件，精準操作
UPDATE user SET age = 20 WHERE id = 1;
DELETE FROM user WHERE id = 1;

-- ? 錯誤：WHERE中使用COUNT(*)
SELECT name FROM user WHERE COUNT(*) > 2;

-- ? 正確：用HAVING過濾聚合結(jié)果（需搭配GROUP BY）
SELECT gender, COUNT(*) AS user_count FROM user GROUP BY gender HAVING user_count > 2;

-- ? 錯誤：name不是分組字段，也不是聚合函數(shù)
SELECT name, gender, COUNT(*) FROM user GROUP BY gender;

-- ? 正確1：將name加入分組
SELECT name, gender, COUNT(*) FROM user GROUP BY gender, name;

-- ? 正確2：用聚合函數(shù)包裹name
SELECT MAX(name), gender, COUNT(*) FROM user GROUP BY gender;

-- ? 錯誤：LIKE后面無通配符，等價于 WHERE name = '張'
SELECT name FROM user WHERE name LIKE '張';

-- ? 正確：搭配%，匹配包含“張”的所有名字
SELECT name FROM user WHERE name LIKE '%張%';

-- ? 錯誤：字符串值未加引號
INSERT INTO user (name) VALUES (張三);
SELECT name FROM user WHERE name = 張三;

-- ? 正確：字符串值加英文單引號
INSERT INTO user (name) VALUES ('張三');
SELECT name FROM user WHERE name = '張三';

-- ? 錯誤1：INSERT語句VALUES后面遺漏括號
INSERT INTO user (name, age) VALUES '張三', 20;

-- ? 錯誤2：多條件AND連接時，多余逗號
SELECT name FROM user WHERE gender = 1, AND age > 20;

-- ? 正確
INSERT INTO user (name, age) VALUES ('張三', 20);
SELECT name FROM user WHERE gender = 1 AND age > 20;